Space closure by frictionless mechanics 2 /certified fixed orthodontic courses by Indian dental academy


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Space closure by frictionless mechanics 2 /certified fixed orthodontic courses by Indian dental academy

  2. 2. Introduction: Space closure is an important step in mechanotherapy, solely dictated by clinical treatment objectives and is irrespective of method employed Space closure should be individually tailored based on the diagnosis & treatment plan Selection of any method should be based on desired tooth movement
  3. 3. Goals for any space closure method Differential space closure capability Axial inclination control Control of rotation & arch width Optimum biological response Minimum patient cooperation Operator convenience
  4. 4. Determinants of space closure Amount of crowding Anchorage Axial inclination of canine & incisors Midline discrepancy & L/R symmetry Vertical dimensions
  5. 5. Amount of crowding: Extractions are Usually done to relive crowding In case of severe crowding anchorage control becomes very crucial Maintaining anchorage while creating space for decrowding is important
  6. 6. Anchorage: Anchorage classification & concept of differential anchorage is important. Using the same mechanics for different anchorage need limits the results Reinforcement methods can be used in critical anchorage situations. Using a force system determined appliance design can improve chances of success.
  7. 7. Axial inclination of canines & incisors Inclination of canine and incisor are particularly important. When same force and moment applied to a tooth or a group of teeth with different axial inclination will result in different type of tooth movement. Example in case of unfavorable positioned canine(root mesial crown distal)
  8. 8. Axial inclination of canines & incisors
  9. 9. Midline discrepancy & L/R symmetry: Mid line discrepancies with or without an asymmetric L/R occlusal relationship corrected as early as possible Asymmetrical forces on L/R could result in unilateral vertical forces, skewing of dental arch or asymmetrical anchorage loss. Vertical dimensions: Undesired vertical forces may result in ↑ Lower Facial Height, ↑ interlabial gap & excessive gingival display.
  10. 10. Minor & major cuspid retraction: Depend upon severity of crowding in anterior segment, anchorage requirements & axial inclination of canine • Minor : refers to uncontrolled tipping of canine when 1-2 mm arch length is required per side (lace back) • Major :controlled tipping or translation of canine when more than 3 mm arch length is required per side. • If canine inclination is ideal then translation is preferred
  12. 12. Retraction mechanics divided into • Sliding (Frictional) mechanics involves either moving the brackets along the arch wire or sliding the arch wire through bracket & tube • Loop (Frictionless) mechanics involves movement of teeth without the brackets sliding along the arch wire but with the help of loops
  13. 13. Moderate Anchorage situation Treatment with 18- slot: either sliding or loop mechanics can be used. Single or narrow twin brackets on canine & PM is ideally suited for use of closing loops in continuous arch wire Treatment with 22- slot: As a general rule space closure done in two steps First retracting the canine usually with sliding mechanics 2nd retracting four incisors usually with closing loop Enmasse – using Opus or T loop but less than ideal
  14. 14. Maximum Anchorage situations Treatment with 18- slot: Friction from sliding is usually avoided, and employing closing loops preferred. Anchorage is augmented & anchorage strain is reduced by: Adding stabilizing lingual arch. Reinforce maxillary posterior anchorage with Extra-Oral force. Class III elastics from high pull head gear to supplement retraction force in lower arch Retraction of canine independently, preferably using a segmental closing loop & then retracting incisors with 2nd closing loop.
  15. 15. Maximum Anchorage situations Treatment with 22- slot: Like 18 – slot Anchorage is augmented & anchorage strain is reduced Canine can be retracted with sliding by Reinforcing posterior anchorage with extra oral force Application of extra oral force directly against canine to slide them posteriorly. Use of segmented arch mechanics for retraction Segmented arch mechanics for tipping/ uprighting
  16. 16. Minimum Anchorage situations Requires anchor control, to reduce incisor retraction by: By incorporating as many teeth in anterior segment Locating the extraction site more posteriorly. Placing active lingual torque in incisor section of archwires To breakdown posterior anchorage(moving one tooth a time) Use of extra-oral force (face mask) Use of implants/ onplants to protract posteriors.
  17. 17. Retraction methods: 1. Staged approach: Methods of canine retraction: Friction Frictionless: Paul Gjessing spring, Burstone T loop, Delta loop, L loop, Omega loop Extra oral: Head gear - Four hooked for both the arches Other methods: Retraction using Rare earth magnets Rapid canine retraction through Distraction of PDL
  18. 18. Staged approach: Methods of en-masse retraction of four incisors: Friction Frictionless : P.G spring, Burstone T loop, Delta loop, L loop, Retraction utility arch, Omega loop arch wire or Closing loop arch wire Extra oral : Head gears Intrusion & retraction of four incisors: Burstone three piece intrusion arch Rickets Retraction & intrusion utility arch
  19. 19. 2. Enmasse retraction of six anteriors: Friction Frictionless – Closing loops, Burstone T loop continuous arch wire, Opus loop (Siatkowaski) Simultaneous retraction & intrusion of six anteriors: K - Sir Arch
  20. 20. Sliding / Friction Mechanics: Tooth is retracted or slides through the arch wire, it involves either moving the brackets along the arch wire or sliding the arch wire through bracket & tube. It is used for both individual canine and enmasse Retraction Friction is present due to surface irregularities of arch wire and bracket
  21. 21. Various methods used: Elastic modules with ligature wire Elastomeric chains Stainless steel Closed coil springs NiTi Co-Cr-Ni J hook head gear Mulligan V bend sliding mechanics Employing tip-Edge brackets on canines.
  22. 22. Advantages: Minimal wire bending time More efficient sliding of arch wire through posterior bracket slots No running out of space for activation Patient comfort Less time consumption for placement
  23. 23. Disadvantages of sliding mechanics: 1. Variable force. 2. Confusion regarding ideal force levels. 3. E-chain absorbs water and saliva when exposed to oral environment causing degradation of force by 50%-70% by the 1st day. 4. Excess Stretching of E-chain causes breakdown of internal bond leading to permanent deformation. 5. Tendency of overactive elastic causing initial tipping & inadequate rebound time for uprighting if forces are activated too frequently
  24. 24. Disadvantages 6. Staining of E-chain 7. Dependent on patient cooperation in case of elastic bands 8. Due to friction and binding between bracket and arch wire applied force should be higher than the required optimum force because of decay in force 9. Generally slower than loop mechanics due to friction Due to all these problems in friction or sliding mechanics, frictionless mechanics stands in better position for retraction, as monitoring of optimum force can be done effectively and it is active for a longer duration of time.
  25. 25. Loop / Frictionless Mechanics: Loop (Frictionless) mechanics involves movement of teeth without the brackets sliding along the arch wire but with the help of loops Force generated intrinsically by arch wire By incorporating loops in arch wire Energy is stored in loops and release it in slow and continuous fashion There is no friction between archwire and bracket
  26. 26. Biomechanics of frictionless mechanics: The teeth in an arch wire will invariably assumes the passive position of the arch wire. When a bend is placed in the middle of the archwire and engaged into brackets two equal and opposite moments are produced When offset bend is placed differential moments are produced. (as anchor bend in Begg technique.)
  27. 27. Biomechanics Greater clockwise moment (extrusion) in posterior segment (near to the v- bend) & smaller anti-clockwise moment (intrusion force) in anterior segment (away from the v- bend) is produced.
  28. 28. This same principles apply in Frictionless mechanics where instead of a bend a loop is placed in the wire. Bends are placed on the mesial & distal legs of loop, called Alpha (α) & Beta (β) bends respectively. These bends produce Alpha and Beta moments when wire is placed into bracket
  29. 29. If β moment > α moment Biomechanics anchorage enhanced by mesial root movement of posterior segment posterior extrusion & anterior Intrusion If α moment > β moment anchorage of anterior segment is increased by distal root movement anterior Extrusion & posterior Intrusion If both equal no vertical force
  30. 30.
  31. 31. Biomechanics Moment is determined by the loop design Activation of loops produces the force in frictionless mechanics. Activated by pulling the distal end of wire through molar tube and cinching back or by soldering a tie back mesial to molar tube on archwire
  32. 32. Biomechanics Moment to force ratio (M/F) determines the type of tooth movement. Moment to force ratio for various tooth movements: M/F Ratio Tooth movement 5:1 - Uncontrolled tipping 8:1 - Controlled tipping 10 : 1 - Translation >10 : 1 - Root movement
  33. 33. Biomechanics According to Charles Burstone - moment to force ratio for translation is about 10:1. A regular 10mm high vertical loop offers a M:F ratio of only 3:1 when it is activated by 1mm. To get M:F ratio of 10:1, activation should be reduced to 0.2mm, but the force level is not sufficient for retraction
  34. 34. Biomechanics M/F could be increased by (Burstone & Koenig) By ↑ vertical dimension of loop (but it has limitation as available space in the vestibule) ↑ horizontal dimension in apical part of loop ↑ Apical length of the wire Helix incorporation Angulations of loop legs ↓ inter bracket distance Positioning loop close to tooth to be retracted bodily
  35. 35. Biomechanics The most effective way to increase M:F ratio is placing Pre Activation Bends Or Gable Bends. These bends can be placed within the loops or where loop meets the arch wire. As we try to engage the wire into bracket we pull the horizontal arm of the loop down producing a moment called the activation moment and the loop is said to be in NEUTRAL POSITION
  36. 36. Biomechanics The M:F ratio increases as spring gets deactivated as the space closes. Sequence of tooth movement with changes in M/F ratio: Controlled tipping (8:1) Translation (10:1) Root movement (12:1) So spring should not be activated too frequently
  37. 37. SPACE CLOSING LOOPS Design considerations: Closing loop arch wires should be fabricated from rectangular wire to prevent wire from rolling in the bracket slot The performance of the loop, from the perspective of engineering theory, is determined by 3 major characteristics 1. Spring properties 2. Moment it generates 3. Its location [William. R. Proffit]
  38. 38. 1. SPRING PROPERTIES The amount of force it delivers and the way the force changes as the teeth move. It is determined almost totally by the Wire material - Stainless steel - Beta-Titanium Size of the wire Distance between points of attachment distance between bracket amount of wire incorporated
  39. 39. Changing the size of the wire produce largest change in its characteristics, but the amount of wire incorporated in the loop is also important [William. R. Proffit]
  40. 40. 2.Moment it generates To close an extraction space while producing bodily tooth movement closing loop must generate not only closing force but also appropriate Moments to bring the root apices together This requirement to generate a movement limits the amount of wire that can be incorporated to make a closing loop springier, because if the loop becomes too flexible, it will be unable to generate the necessary moments
  41. 41. Loop design is also affected. Placing some of the wire within the closing Loop in a horizontal rather than vertical direction improves its ability to deliver the moments needed to prevent tipping. To generate appropriate moments additional moments must be generated by Gable bends
  42. 42. 3.Its location: Its location is very important for its performance in closing space. As gable bends are incorporated, the closing loops functions as the V bend in the arch wire. Effect of V bend is very sensitive to its location There can be 3 locations of V bend 1.Equal distance 2.Closure to anterior 3.Closure to Posterior
  43. 43. If it is in the center of the span a V-bend produce: Equal forces and Equal couples on the adjacent teeth
  44. 44. If it is one-third of the way between adjacent brackets, the tooth closer to the loop - extruded & moment - root toward the V-bend, tooth farther away - intrusive force but no moment
  45. 45. 4.Additional design principle Fail safe: this means that, although a reasonable range of action is desired from each activation, tooth movement should stop after that, even if patient does not come for scheduled appointment. Design should be as simple as possible During activation of loop it is considered more effective when it is closed rather than opened
  46. 46.
  47. 47. INDIVIDUAL CANINE RETRACTION: It is important to do individual canine retraction in maximum anchorage cases. Correct positioning of the canine after retraction is imperative for function, stability and esthetics This requires the creation of a bio mechanical system to deliver a predetermined force and a relatively constant moment-to-force ratios in order to avoid distal tipping and rotation.
  48. 48. For translation of canine : The displacement of canine depends on the relationship between the line of force and the center of resistance (CR) Application of force through CR.
  49. 49. Distal tipping Force application
  50. 50. Rotation Force application
  51. 51. Anti-tip and anti-rotation moment-to-force conditions necessary for translation of canines with average dimensions. Anti-Tip:- 11:1 Anti-Rotation:- 4:1
  52. 52. Force application Anti tip couple
  53. 53. Anti rotational couple Force application
  54. 54. VARIOUS CANINE RETRACTION SPRINGS: 1. T-loop spring (Burstone - AJO/1976) 2. Cuspid retractor (Rickett - AJO/76) 3. P.G spring (P. Gjessing - AJO/1985) 4. Cuspid retractor (R. Haskell - AJO/1990) 5. Nickel-Titanium canine retraction Spring (Yasoo Watanabe - JCO/2002 )
  55. 55. T-LOOP SPRING: (BURSTONE/AJO/1976) Burstone called it the Attraction Spring used for: Canine Retraction - severe crowding cases and high anchorage (group-A) cases. Enmasse Retraction - four incisors after canine retraction
  56. 56. T-LOOP SPRING: Wire selection for loop: 18- slot: 16 x 22 SS or 17 x 25 TMA 22- slot: 18 x 25 SS or 19 x 25 TMA Base arch wire: 21 x 25 in SS
  57. 57. Neutral Position: Activated position: The pre-activated spring with the anti tip (M/F- 11:1) and anti rotation (M/F- 4:1) is placed Activated by pulling it and giving a distal cinch back. Activation on insertion is 6- 7mm
  58. 58.
  59. 59. Activation on insertion is 6-7mm The M/F ratio is 8:1 – controlled tipping Now as the tooth moves the activation reduced to 4mm the force is reduced. M/F ratio is further increased to 10:1 - bodily movement The activation is reduced to 2mm – force is further reduced M/F ratio increased to 12:1 – root uprighting So spring should not be activated too frequently Spring usually activated every 4-6 weeks
  60. 60. Composite T loop attraction spring: Composite TMA 0.018 - 0.017 x 0.025 in retraction spring. A 0.018 in round T spring is welded directly to a 0.017 x 0.025 in base archwire. Used in the segmented arch technique for both canine and enmasse retraction.
  61. 61. CUSPID RETRACTOR: (RICKETT’S/AJO/1976) Developed by Ricketts in Scotland in 1976. Rate of canine retraction by Ricketts was 1.38mm/month Additional effects: - Mesial crown tipping - Disto-palatal rotation
  62. 62. POUL GJESSING CANINE RETRACTION SPRING: (P.GJESSING/AJO/1985) . Poul Gjessing of Denmark 1985 . The spring is constructed to resist rotational and tipping tendencies during retraction
  63. 63. Loop Configuration: made from: 016 x 022 in SS wire. predominant element - OVOID DOUBLE HELIX LOOP extending 10 mm apically, and 5.5 mm in width. smaller occlusal loop - 2 mm diameter, incorporated to lower the levels of activation. Anti-tip bend (Alpha) 15˚. Beta-bend 12˚ for II premolar, 30˚ for I molar. Anti rotation bend 35˚. Distal sweep for molar.
  64. 64. PG CANINE RETRACTION SPRING 35º Anti rotation bend 5.5 mm Apical loop 30º 15º Beta bend Anti tip bend 12º 2 mm Occlusal loop
  65. 65. Spring design: Ovoid Double Helix Loop - reduce the load deflection of the spring Placed gingivally - activation will cause a tipping of the short horizontal arm (attached to the canine) In a direction that will increase the couple acting on the tooth. Smaller loop - occlusally - lower levels of activation on insertion in the brackets in the short arm (couple) Formed so that activation further closes the loops.
  66. 66. sweep in the distal leg - eliminates undesirable ß moments acting at second premolar bracket (which tend to move the root apex too far mesially) Activation: By pulling the distal, horizontal leg through the molar tube. Force level of approximately 160 gm is obtained when the two sections of the double helix are separated 1 mm. Activation is repeated every 4 weeks, and the canine is expected to undergo approximately 1.5 mm of controlled movement with each activation.
  67. 67. CUSPID RETRACTOR: (R.HASKELL/AJO/1990) Specially designed 0.017 x 0.022 inch heat-treated Elgiloy springs (Rocky Mountain Orthodontics, Denver, Colo.)
  68. 68. inserted into buccal and gingival tubes, which are part of the molar and canine brackets special canine brackets
  69. 69. Spring design: similar to traditional retraction springs except for the extra helix in the anterior (a) portion. helix, in conjunction with the gables placed in the posterior (b) legs of the spring, provides the required couple "counter-moment" for the moment of the force allows for the translation of the canine or molar during space closure.
  70. 70. • Three angles in the spring to consider • Ø1 and Ø2 - bends posterior & anterior to contraction helices • Ø3 - angle of the anterior leg of the helix. Mandibular model • Ø1 Ø2 • 45° 45° • 45° 45° • 45° 45° Ø3 0° - Anterior retraction 15° - Reciprocal attraction 30° - Posterior protraction Maxillary model • Ø1 • 45° • 45° • 45° Ø3 15° - Anterior retraction 30° - Reciprocal attraction 45° - Posterior protraction Ø2 45° 45° 45°
  71. 71. NITI CANINE RETRACTION SPRING: (Yasoo Watanabe, JCO/2002) Made from .016" ×.022" Titanal wire, with anti-tip and antirotation bends incorporated in closing loop.
  72. 72. Clinical implications: Major advantage of this spring is the ability to use it without a preliminary leveling stage, Because it can simultaneously retract the canines and level the posterior teeth. Its light, continuous force allows an activation of as much as 10mm to complete canine retraction without reactivation of the closing loop. Spring provides continuous forces and moments over a broad range of activation. And the closing force can be maintained within normal biological and physiological limits.
  73. 73.
  74. 74. EN-MASSE RETRACTION: Retracting group of teeth together as a single unit. Can effectively be employed in moderate and minimum anchorage cases Simultaneous intrusion and retraction of the anterior teeth, maintaining torque control may also be employed En-masse retraction is done with a continuous arch wire with one closing loop each side distal to cuspid. Differential force technique and location of loop can be placed depending on the type of anchorage.
  75. 75. VARIOUS RETRACTION ARCHWIRES: Various loop designs are available for retraction All are having pre-determined vertical heights Ranging from 7-10mm in vertical direction to keep it closure to center of resistance of tooth
  76. 76. OPEN VERTICAL LOOP: Originated by Dr. Robert W. Strang (1933). Used for retraction of anterior teeth CLOSED VERTICAL LOOP: Only being difference is horizontal overlapping.
  77. 77. BULL LOOP: - Dr. Harry bull (1951) Introduced a variation of standard vertical loop Loops legs were tightly abutting each other He recommended that these loops should be made from .0215 x .025 stainless steel
  78. 78. VERTICAL OPEN LOOP WITH HELIX: Dr Morris Stoner Main purpose is to increase the working range
  79. 79. OMEGA LOOP: As mentioned by Dr Morris Stoner Loop named because of resemblance to the Greek letter ‘omega’ The loop is believed to distribute the stresses more evenly
  81. 81. DELTA LOOP: It was described by Dr. Proffit. Wire configuration: 0.018 slot - 16 x 22 inch 0.022 slot - 18 x 25 inch Approximately 200 angulations on either side
  82. 82. T-LOOP FOR ENMASSE RETRACTION: Utilizes loops for space closure for 1.Anterior retraction 2.Symmetric space closure 3.Posterior protraction
  84. 84. ASYMMETRICAL ‘T’ LOOP: - JAMES. J. HILGERS (JCO/1992) made of .016“ x 022" TMA (for .018" brackets) or .0l9“ x 025" TMA (for .022" brackets), with 5mm vertical step, 2mm anterior loop, and 5mm posterior loop. archwire should have - exaggerated reverse curve of Spee & strong distal molar rotation
  85. 85. Pre activation of Asymmetric "T" loop: A. Short mesial loop compressed B. Long distal loop opened. C. Loop after pre activation.
  86. 86.
  87. 87. Broussard combination closing and bite opening loop with step between anterior and posterior segments.
  88. 88. Hilgers modification with reduced loop size for patient comfort and crossed "T" for greater mechanical efficiency.
  89. 89. Mushroom loop: Apical addition of wire in Archial configuration More patient friendly- reduces the horizontal part of wire near vestibule Beta-titanium CNA M loop- 0.017 x 0.025 in Activation up to 5 mm Reactivation- every 6-8 wks Bypass premolars - ↑ IBD
  90. 90. Preformed M loop space closing archwires: Pre activation- separating the legs by 3mm. Gable bends - mesial to increase anterior moment - distal to increase anchorage moment Torque in distal leg eliminated - wire passive in 3rd order in buccal segment Loop reactivated until there is at least 3 mm of space closure After space closure, wire left in mouth for 1-2 visits- root uprighting
  91. 91. Double keyhole loop: Roth treatment mechanics Introduced by John Parker - 0.019 x 0.026 in Concept: Complete space closure with one set of archwires Allows operator to select how space will be closed Activation- cinching wire distal to last molar tube, activated every 3-4 weeks
  92. 92. POUL GJESSING RETRACTION ARCH: - P.GJESSING (AJO/1992) The PG retraction spring can be used as a module for controlled retraction of both canines and incisors. The suggested horizontal force - 100 gm for incisor retraction The incisor segment intrusion is induced with a magnitude of 10 to 25 gm on each side between subsequent activations
  93. 93. Design: Similar to canine spring with some modifications. Includes vertical slot in the lateral incisor bracket. 750 bend 3mm mesial to the helix to be inserted in the vertical slot Activated by pulling distal end separating the double helix and producing 100gms force. Activated every 4-6 weeks
  94. 94. OPUS LOOP: - RAYMOND.E.SIATOWSKI (AJO/1997 ) Used for en-masse retraction of all six anterior Teeth Wire sizes: 0.016 X 0.022 S.S, or 0.018 X 0.025 S.S. wire. 0.017 X 0.025 inch TMA
  95. 95. Development of opus loop: M/F required for translation Individual teeth: 7.1-10.2 mm Groups of teeth: 8.0-9.1 mm Most closing loops have inherent M/F 4-5 mm or less To achieve net translation, need to add residual moments Gable bends anterior & posterior Posterior gable bend & anterior wire-bracket twist
  96. 96. Development of opus loop: Disadvantage of gable bend: Cycle of Tipping- translation- uprighting (lower Young's Modulus materials go through fewer of these cycles for a given distance of space closure). Correct magnitude of residual moments are difficult to achieve Changing areas of stress distribution in the pdl may not yield most rapid, least traumatic method of space closure
  97. 97. Development of opus loop: Study: design and verify loop design capable of delivering M/F inherently without adding residual moments. Castigliano’s Theorem: to derive M/F ratio in terms of loop geometry. Using Castigliano's theorem, and refined, using FEM simulations, and verified experimentally a new design, the Opus Loop was developed. capable of delivering a target M/F within the range of 8.09.1 mm inherently, without adding residual moments.
  98. 98. Advantages: more precise force systems with non varying M/F can be delivered Groups of teeth therefore can be moved more accurately en masse space closure with uniform PDL stress distributions more rapid tooth movement with less chance of traumatic side effects neutral position is the same as the inactivated position - allows known forces systems to be applied to the teeth Disadvantages: loops must be bent accurately to achieve their design potential. All the dimensions are critical to the performance of the loop
  99. 99. TRANSLATION ARCH: - ROBERTO MARTINA (JCO/1997 ) kind of utility arch - simultaneously retract, torque, and intrude or control the extrusion of the maxillary incisors. made of .016" × .022" TMA for .018" bracket slots anterior segment inserted into incisor brackets, and two buccal segments into gingival first molar tubes Two loops - connect the anterior and posterior segments - extended as far vertically as possible
  100. 100. A distal activation of 2mm on each end of the arch will produce the 100g of horizontal force needed for incisor retraction To achieve a moment-to-force ratio of 10, placing a 3rd-order activation (root-palatal torque) in the anterior segment of the arch.
  101. 101. 3rd-order activation should produce an intrusive force of about 20g on each molar. Extrusive force exerted on the anterior teeth. To compensate this side effect - tipback / arc (preferably) bent into each buccal segment to produce an intrusive force
  102. 102. K-SIR ARCH: - VARUN KALARA(JCO/1998) K-SIR: Kalra Simultaneous Intrusion and Retraction archwire continuous .019" X .025" TMA archwire with closed 7mm X 2mm U-loops at the extraction sites
  103. 103. To obtain bodily movement and prevent tipping of the teeth into the extraction spaces, a 90° V-bend is placed in the archwire at the level of each U-loop Centered 90° V-bend creates two equal and opposite moments that counter tipping moments produced by activation forces.
  104. 104. Off-center 60° V-bend placed about 2mm distal to U-loop. Off-center V-bend creates greater moment on molar, increasing molar anchorage and intrusion of anterior teeth. 20° anti-rotation bends placed in the archwire just distal to U-loop
  105. 105. A trial activation of the archwire is performed outside the mouth trial activation releases the stress built up from bending the wire and thus reduces the severity of the V-bends Neutral position of loop determined with mesial and distal legs extended horizontally. In neutral position, loop is 3.5mm rather than 2mm wide.
  106. 106. The archwire is inserted into the auxiliary tubes of the first molars and engaged in the six anterior brackets Second premolar bypassed - ↑ IBD First molar and second premolar are connected by segment of .019" X .025" TMA wire It is activated about 3mm, so that the mesial and distal legs of the loops are barely apart
  107. 107. archwire exerts 125 gm intrusive force on anteriors & similar amount of extrusive force distributed between two buccal segments archwire should not be reactivated at short intervals, but only every six to eight weeks until all space has been closed. Advantages: Simplicity of design- ease of fabrication Comfortable to the patient TMA- low forces, low LDR, long range of action En masse retraction- Shortens treatment time- prevents appearance of unsightly space distal to incisors.
  108. 108. CONCLUSION A good understanding of mechanics is required when using retraction loops or springs, because minor errors in mechanics can result in major errors in tooth movement
  109. 109.